In recent years, as the use of wireless terminal devices has dramatically increased, the amount of communication that is relayed by relay devices such as repeaters is also steadily increasing. Consequently, when a wireless terminal device performs communication with another wireless terminal device, a distributed trunking method wireless communication system that selects at least one of a plurality of relay devices that are connected together via specified communication lines has become widely used. Furthermore, wireless terminal devices are also known that have both a talk-around function for direct communication between wireless terminal devices without via a repeater, and a trunking function.
A wireless terminal device that has a trunking function and talk-around function can be switched by user control from the trunking method, in which a repeater relays communication, to the talk-around method, in which direct communication is performed between wireless terminal devices, when leaving the coverage area of a repeater, or in other words, when out of range. In order to omit this kind of user operation, a function is proposed in which when transmission to a repeater by a wireless communication device using the trunking method fails, the communication method is automatically switched to the talk-around function. For example, in Patent Literature 1, the wireless communication device comprises an external connector and microcomputer, and inputs and stores a trunk system communication instruction signal that gives an instruction to perform communication using the trunked system (trunking method) that is provided via the external connector, a TA communication instruction signal that gives an instruction to perform communication using the TA (talk-around) function, and a frequency instruction signal that gives an instruction for the transmitting frequency. The wireless communication device is constructed such that when an instruction is given to perform trunked system communication, the wireless communication device performs transmission processing via a repeater at a transmitting frequency based on the frequency instruction signal, and when a state in which there is no signal from the repeater within a predetermined period continues several times, the wireless communication device sets the receiving frequency to the transmitting frequency of the intended communicating party, sets the transmitting frequency to the receiving frequency of the intended communicating party and performs communication using the talk-around function.    Patent Literature 1: Unexamined Japanese Patent Application KOKAI publication No. 2007-60071.
In the technology disclosed in Patent Literature 1, after transmission to a repeater, when a state in which there is no signal back from the repeater within a specified period of time continues several times, communication is performed using the talk-around method, and when a signal is received back from the repeater, communication is performed using the trunking method. However, when communication is performed between a wireless terminal device having a relatively high level of transmission power (for example a mobile type of device) and a wireless terminal device having low transmission power (for example, a battery-operated portable type of device), as both terminals separate from the repeater and are located in the vicinity of the boundary between being in the coverage area and being out of range, deterioration of the communication quality may occur. In the vicinity of the boundary, the wireless terminal device having large transmission power is able to transmit an uplink signal to the repeater as well as receive a downlink signal from the repeater; however, even though the wireless terminal device having low transmission power may be able to receive a downlink signal from the repeater, an uplink signal may not reach the repeater. Particularly, in the so-called fringe area, which is the vicinity of the boundary between being in the service area and being out of range where the radio wave environment is unstable, deterioration of the communication quality remarkably occurs. Therefore, by switching between the trunking method and the talk-around method by just whether or not a downlink signal is detected from the repeater as in the technology of Patent Literature 1, this problem cannot be solved. Furthermore, when switching between the trunking method and talk-around method in the technology of Patent Literature 1, both the receiving frequency and the transmitting frequency must be changed, so that the time required for switching becomes long, and when communication becomes disrupted, deterioration of communication quality occurs.
The object of the present invention is to solve the aforementioned problems by providing a wireless terminal device, a wireless communication method, and a wireless communication system and program that maintain good communication quality even in communication by a pair of wireless terminal devices having a difference in level of transmission power or in areas where the radio signal environment is unstable.
Moreover, another object of the present invention is to provide a wireless terminal device, a wireless communication method, and a wireless communication system and program that do not require that both the receiving frequency and transmitting frequency be changed when switching between the trunking method and talk-around method.
In order to accomplish aforementioned objectives, the wireless terminal device of a first aspect of the present invention is a wireless terminal device that performs wireless communication with the wireless terminal device of another party via relay by a relay device or directly, comprising: communication permission request means (21, S101 to S104) for receiving a downlink signal that is transmitted from a pre registered specified relay device (home repeater) when requesting communication, specifying an idle channel based on idle channel information that is included in the downlink signal, and requesting communication permission from a relay device that provides the idle channel using the uplink frequency of the specified idle channel; and communication means (CPU 21, S118 to S131) that uses the same frequency as the frequency of the downlink signal from the specified relay device for transmitting a signal to the wireless communication terminal device of another party requesting communication when it is not possible to receive the communication permission from the relay device from which the communication permission was previously requested.
The communication means, for example, can further comprise a response receiving means (FIG. 2; receiving circuit 20, S121) for receiving a response from the wireless terminal device of another party. In this case, for example, the communication means comprises:
determining means (CPU 21, S122) for determining whether or not the response comes directly from the wireless communication terminal device of the other party and not via a relay device;
specification means (CPU 21, S130) for specifying a frequency that can be used when it is determined that the response is a direct response; and
direct communication exchange means (CPU 21, S130) for setting the communication frequency to the specified usable frequency, and exchanging communication with the wireless communication terminal device of the other party.
The communication permission request means, for example, can include means for selecting an idle channel and resending the communication request (S107 to S109, S207 to S208, 203) based on idle channel information that is included in the downlink signal from the specified relay device when communication permission could not be received.
The communication means, for example, comprises means (S120) for matching the receiving frequency and transmitting frequency with the downlink frequency of the specified relay device and transmitting a signal to the wireless terminal device of the other party when communication permission could not be acquired and a downlink signal could not be received after transmitting a communication request (step S106: YES, step S107: NO).
The wireless terminal device can further comprise
means (S218, 219) for waiting a set amount of time after communication permission has been received and the communication means transmits a signal when a downlink signal can be received from the specified relay device but no response is received from the terminal of the other party, and for executing a disconnection process when no response can be received even after waiting a set amount of time.
The wireless terminal device can further comprise means (20, 26) for determining the communication state and outputting information that indicates the communication state.
It is also possible to construct a wireless communication system comprising: a wireless terminal device as described above and a plurality of relay devices.
In order to accomplish the aforementioned objectives, a wireless communication method of a second aspect of the invention is a wireless communication method, comprising steps of:
transmitting a downlink signal from a relay device, the downlink signal including idle channel information;
a wireless terminal device receiving the downlink signal that was transmitted from the specified relay device (home repeater) when requesting communication, specifying an idle channel based on the idle channel information that is included in the downlink signal, and using the uplink frequency of the specified idle channel to request communication permission from the relay device that provides the idle channel,
transmitting a permission signal to the relay device that provides the idle channel when allowing communication; and
the wireless terminal device using the same frequency as the frequency of the downlink signal from the specified relay device to transmit a signal to the wireless communication terminal device of the other party when the communication permission could not be received from the relay device from which the communication permission was previously requested.
In order to accomplish the aforementioned objective, a computer program of a third aspect of the present invention is a computer program that causes a computer comprising a communication function to function as
communication permission request means (21, S101 to S104) for receiving a downlink signal that is transmitted repeatedly from the pre registered specified relay device (home repeater), specifying an idle channel based on idle channel information that is included in the downlink signal, and requesting communication permission to a relay device that provides the idle channel using the uplink frequency of the specified idle channel to request communication permission; and
communication request means (CPU 21, S118 to S131) that uses the same frequency as the frequency of the downlink signal from the specified relay device for transmitting a signal to the wireless communication terminal device of another party requesting communication when it is not possible to receive communication permission from the relay device from which the communication permission was previously requested.
Moreover, this program can be recorded on a recording medium and distributed or circulated.